An electrostatic MEMS switch is a switch operated by an electrostatic charge and manufactured using MEMS techniques. The MEMS switch can control electrical, mechanical, or optical signal flow, and they have application to telecommunications, such as DSL switch matrices and cell phones, Automated Testing Equipment (ATE), and other systems that require low cost switches or low-cost, high-density arrays.
Many MEMS switches are designed to employ a cantilever or beam geometry. These MEMS switches include a movable beam having a structural layer of dielectric material and a conductive/metal layer. Typically, the dielectric material is fixed at one end with respect to the substrate and provides structural support for the beam. The layer of metal is attached to the underside of the dielectric material and forms a movable electrode and a movable contact. The movable beam is actuated in a direction towards the substrate by the application of a voltage difference across the electrode and another electrode attached to the surface of the substrate. The application of the voltage difference to the two electrodes creates an electrostatic field which pulls the beam towards the substrate. The beam and substrate each have a contact which is separated by an air gap when no voltage is applied, wherein the switch is in the “open” position. When the voltage difference is applied, the beam is pulled to the substrate and the contacts make an electrical connection, wherein the switch is in the “closed” position.
MEMS switches having low actuation voltages are very desirable. The required actuation voltage can be reduced by either reducing the gap distance between the two electrodes or increasing the surface area of the electrodes. Assuming that the electrode is occupying a maximum area of the beam, the dimensions of the beam must be increased to accommodate a larger electrode. A problem associated with increasing the length of the beam is that the beam becomes more compliant, thus increasing the likelihood of stiction, i.e., a condition wherein the movable beam will not revert back to an “open” position from a “closed” position. Also, reducing the gap distance between the electrodes can increase the likelihood of stiction. Furthermore, reducing the gap distance between the electrodes can increase the difficulty in forming the protruding contacts because there is less available area beneath the movable beam to do so. Another problem with reducing the gap distance is that any stress and curvature of the beam can lead to contact of the electrodes, thus shorting the electrodes.